while(<DATA>){
    next unless /\w/;                               
    my($server,$datetime,$metric,$value) = (split)[0,1,2,3];
    my $ddhh = substr $datetime,0,16;              
    my $dd   = substr $datetime,0,10;              
    $h{$dd    }{$metric}{max} = $value; # How can I assign Maximum value within the group $dd and $metric ?
	$h{$dd    }{$metric}{min} = $value; # How can I assign Maximum value within the group $dd and $metric ?                              
    $m{$ddhh  }{$metric}{max} = $value; # How can I assign Maximum value within the group $ddhh and $metric ?                              
	$m{$ddhh  }{$metric}{min} = $value; # How can I assign Maximum value within the group $ddhh and $metric ?                              
}